> Now comes the pitch. The "sweet spot" in cluster nodes at the moment seems
> to be a dual socket, dual core Opteron or Intel machine with 2 gigs of RAM
> per core, so each box is a 4-way SMP
> (I will be flayed alive by the list for such cavalier numbers).
merely scourged ;)
I agree with the config you mention for many purposes. I would almost
certainly consider using 4-core chips for a serial cluster, though I don't
know offhand whether dual-socket would be more cost-effective than single.
it's also worth pointing out that the first fork in the decision-tree is
really whether to use desktop or server components. with servers, the
sweet-spot does tend towards 2-socket. there are many attractive things
about this approach, such as frequent builtin dual-gigabit, more robust
components such as ECC, and important managability features such as IPMI.
OTOH, there is some attraction to going cheap (arguably more beowulfy!)
by using desktop-grade single-socket boards/chips. if you take this
approach, you're guided towards some other config details - you probably
won't get ECC, for instance (saving some price, but should be considered).
to be cost-effective, you also need to choose a cheap chassis - desktop
boxes piled on wire racks are reasonable, though there are cheap 1U chassis,
as well. such an approach is cost-sensitive, so you want to configure with
no more ram than necessary and quite possibly no local disk.
> Now, such a box is likely to have oodles (scientific term) more processing
> power than four pentiums.
just some blue-sky numbers: a 5-year old machine will have individual
performance figures which are about 1/4 of todays hardware. that includes
interconnect (gigabit was uncommon then), memory bandwidth, peak flops,
onchip cache, etc. any real app will probably not pin _all_ the components,
but the fractions are multiplicative, so a delivered performance is some
weighted _product_ of the factors. I'd expect somewhere between 5:1 and 20:1.